Dry-running reciprocating vacuum pump

ABSTRACT

A dry-running reciprocating vacuum pump includes at least one pump stage located in the housing and including a cylinder having at least one gas inlet, a gas outlet, and a piston reciprocating in the cylinder and controlling the at least one inlet, a drive system for driving the piston-driving shaft, which is connected by a crank gear mechanism with the piston, and including a plurality of permanent magnets arranged on the shaft and stationary electrical coils surrounding the permanent magnets for producing a rotatable magnetic field, and a control electronics located in the pump housing for operating the coils.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dry-running reciprocating vacuum pump that includes a housing, at least one pump stage located in the housing and including a cylinder having at least one gas inlet, a gas outlet, and a piston reciprocating in the cylinder, with the at least one inlet being controlled by the piston, a shaft located in the housing for driving the piston, a crank gear mechanism connecting the shaft with the piston, and drive means for driving the shaft.

2. Description of the Prior Art

The last several years, dry-running reciprocating vacuum pumps such as, e.g., disclosed in U.S. Pat. No. 5,921,755, obtained an increased commercial importance. They are used for producing low and high vacuum in the fields where the contamination of recipients with oil deposites, even in minute amounts, cannot be tolerated.

The quality of an obtained vacuum depends on the clearance or sealing between the piston and the cylinder. It also depends, in a large degree, on the size of a dead volume. Under the dead volume is understood, e.g., the volume that is left in the compression chamber after the piston reached, in its movement, the upper cusp point and, thereby, the ejection point. The dead volume space results, e.g., from the valve design.

After the gases have been ejected or expelled, a suction process follows during which the piston is displaced away from the upper cusp point, and the compression chamber volume increases. In the increased volume of the compression chamber, a strong vacuum is produced. During the start of the pumping-out process, the piston is displaced against the atmospheric pressure. As a result, the pressure between the piston bottom and the piston cover drops by about 1 Bar. This requires an adequate torque at the drive motor side in order to be able to displace the piston.

Often the conventional reciprocating vacuum pumps are so formed that the space with the crank gear mechanism is also evacuated in the course of pumping the gas out. During a subsequent course of pumping-out, this pressure difference is reduced and, thereby, the requirement to the necessary torque of the drive motor is also reduced. The available torque depends on the power consumption of the drive motor.

The state-of-the art reciprocating vacuum pumps are driven by alternating current electrical motors. These motors have a low rotational speed and, correspondingly, a low torque. Therefore, these motors should be very large, much more powerful than it is necessary for continuous duty. This results in high operational costs due to a large but unnecessary energy consumption.

Further, the over dimension leads to a need in a large space requirement. However, contrary to this, there is a tendency to form the pumps as small as possible. Also, the large size of the electric motor causes an increased vibration of the pump which at present is tolerated less and less in modern pump stands and plant equipped with sensitive measuring apparatuses. In many cases, it is desirable to be able to control the suction capacity of a pump. To this end, control electronics is needed which further increases manufacturing costs.

Accordingly, an object of the invention is a dry-running reciprocating vacuum pump in which the drawbacks of the state-of-art pump are eliminated.

SUMMARY OF THE INVENTION

This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a dry-running reciprocating vacuum pump the drive means of which includes a plurality of permanent magnets arranged on the pump shaft and stationary electrical coil means surrounding the permanent magnets for producing a rotatable magnetic field, and control electronics located in the housing for operating the coil means. The inventive reciprocating vacuum pump is driven by a brushless direct-current motor which is formed by the permanent magnets, which are secured on the pump, and stationary electrical coils which produce a rotatable magnetic field. The coils are controlled and are supplied with current by the control electronics. The advantage of the inventive motor in comparison with motors, which are used in conventional pumps, consists in smaller dimensions of the motor because brushless direct current motors have a high torque already at a low rotational speed. They are characterized by a smaller power consumption which reduces heating of the pump and its vibration. The control electronics, which powers and controls the coils, can be so formed that it would control the rotational speed and, thereby, the suction capacity of the pump.

The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of the preferred embodiment, when read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawings:

Single FIGURE shows a schematic view of a reciprocating vacuum pump according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A reciprocating vacuum pump 1 according to the present invention, which is shown in the drawing, has a housing 2 in which there is located a shaft 12 supported in bearings 13. On the shaft 12, there is arranged a plurality of permanent magnets 14 which are surrounded by coils 10 that generates a rotatable magnetic field. The rotation is produced by an electronic commutation. For generation of a commutation signal, there is provided control electronics 8 having a power element 9 for operating the coils 10. Position sensors 16 permit the control electronic 8 to determine the shaft angular position. The position sensor 16 can be formed, e.g., as Hall sensors. The control electronics 8 is located in a removable housing part and, in addition to the power element 9, has a control element. The pump 1 can be connected with a voltage source. As a voltage source, e.g., an industrial voltage network (24V or 48V), an alternating voltage network of 230V, or any other conventional supply network can be used. Via a crank gear mechanism, the shaft 12 drives a piston 20, periodically changing the volume of a compression chamber 26. The compression chamber 26 is formed by a cylinder in a head of which there are provided a gas inlet 22 and a gas outlet 24 which are equipped with appropriate valves. In the lower portion of the cylinder, there is provided a further gas inlet 23, opening and closing of which is controlled by the piston 20. The further gas inlet 23 is open only when the piston 20 reaches the lower cusp point.

According to an advantageous embodiment of the present invention, the control electronics 8 is so formed that the reciprocating vacuum pump 1 can be driven with different rotational speeds. According to one of the embodiment of the present invention, the inventive reciprocating vacuum pump is formed as a multistage reciprocating vacuum pump.

According to a further embodiment of the present invention, the control electronic 8 can operate with one- or multi-phase network voltage between 60V and 400V. A selector switch permits to select a respective voltage. It is advantageous when the control electronics 8 is provided with means that automatically recognizes the supply voltage which is applied. The foregoing means insure that the inventive dry-running reciprocating vacuum pump can operate with all voltages used throughout the world. As a result, high mounting costs can be spared as the pump need not be adapted to special local conditions. Instead, standard components can be used for a pump that can operate worldwide.

As it has already been discussed above, the control electronics 8 contains a power element 9 for operating the coils 10. It is advantageous when the power element 9 forms a thermal contact with the wall of the housing 2. In this case, the heat from the pump 1 is removed by thermal convection, which permits to eliminate additional cooling means.

According to one of the embodiment of the invention, the housing part, which contains the control electronics 8, forms part of the pump housing 2.

Though the present invention was shown and described with references to the preferred embodiment, such is merely illustrative of the present invention and are not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is therefore not intended that the present invention be limited to the disclosed embodiment or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims. 

1. A dry-running reciprocating vacuum pump, comprising: a housing; at least one pump stage located in the housing and including a cylinder having at least one gas inlet, a gas outlet, and a piston reciprocating in the cylinder, the at least one inlet being controlled by the piston; a shaft located in the housing for driving the piston; a crank gear mechanism connecting the shaft with the piston, a drive system for driving the shaft and having a plurality of permanent magnets arranged on the shaft, and stationary electrical coil means surrounding the permanent magnets for producing a rotatable magnetic field; and a control electronics located in the housing for operating the coil means.
 2. A dry-running reciprocating vacuum pump according to claim 1, further comprising sensor means for determining a position of the shaft.
 3. A dry-running reciprocating vacuum pump according to claim 2, wherein the sensor means comprises Hall sensor means.
 4. A dry-running reciprocating vacuum pump according to claim 1, wherein the control electronics is directly connectable with a supply network.
 5. A dry-running reciprocating vacuum pump according to claim 4, wherein the control electronics is connectable with one- or multi-phase voltage between 60V and 400V.
 6. A dry-running reciprocating vacuum pump according to claim 1, wherein the control electronics comprises means for recognizing an applied network voltage and means for switching voltage regions.
 7. A dry-running reciprocating vacuum pump according to claim 1, wherein the control electronics comprises a power element for operating the coil means and forming a thermal contact with a wall of the pump housing. 